Pulverizing mill



Sept. 7 1926.

A. M. READ PULVERIZING MILL original Filed DGO 51' .1919

JNVENTOR fxmh/M Sw N ATTORNEY Patented Sept. 7, 1926.

UNITED STATES l Y 1,598,933 -PATENT OFFICE.

ALEXANDER MAHAIFEY BEAD, F ooLirMBUs, OHIO.

PULvEnIzING MILL. A

Original application led December 3l, 1919, Serial No. 348,506. Dividedand this application nled. October 9, 1920, Serial Fo. 415,808. RenewedNovember l, 1924.

The present invention relates to certain new and useful improvements inpulverizing mills of the class in which each consists of a rotatablebarrel wherein the material to be pulverized may be tumbled about withfreely movable crushing bodies and be pulverized by contact therewith.

In my co-pending application, Serial No. 348,506, filed December 31st,1919, of which this application is a division, I have disclosed apulverizing mill comprising a barrel adapted to revolve about itslongitudinal axis which is so disposed to the horizontal that theincluded material will tend to travel on the lower side of said barrelfrom the receiving to the discharging end of the mill, and in which thebarrel is divided into a series of grinding compartments whereby thematerial is so classified that the coarser fragments are retained in theforward compartment while the iiner particles are passed progressivelythrough thesucceeding compartments towards the delivery end of thevmachine.

The especial object of this invention is to provide a machine of theclass described wherein the barrel is divided into a series ofpulverizing chambers by partition screens of improved construction whicheffectively retain the oversize material in the respective pulverizingchambers without undue 0bstruction to the longitudinal flow of the linematerial through the mill.

The means by which I attain this object is fully set forth in thefollowing specification and illustrated in the accompanying Idrawingwhich is a longitudinal vertical section of the preferred embodiment ofmy inventiOn.

As shown in the drawing the numeral l indicates a barrel adapted torevolve about its longitudinal axis which is so disposed to the`horizontal that material within the barrel will tend to travel on thesides of the barrel-from the receiving to the delivery end of the millas the barrel revolves. To the barrel 1 is attached the bearing rings 2and 3 which bear upon the rollers 4 and 5 to support the barrel forrotation. The rollers 4: and 5 are mounted in suitable journal bea-ringsG and 7 which are supported upon the foundation of the mill. To thebarrel 1 is attached a ring gear 8 which is engaged by a pinion 9. Thepinion 9 is mounted upon apower shaft from which power is derived torevolve the barrel. The upper end of .the barrel 1 is closed by a plate10 to which is secured a cylindrical extension 11. The extension 11 isjournaled in a pillow block 12 supported upon the foundation casting 13.The pillow block'12 is provided with the customary removable cap 14. inwhich is formed a lubricant receptacle 15. 16 is a ball bearinginterposed between the outer end of the pillow block 12 and the ange 17of the cylindrical extension 11 to prevent longitudinal movement of thebar? rel. This cylindrical extension 11 and the plate 10 are pierced byal central bore through which extends a cylindrical trough 18 formed atthe lower end of the feed hopper 19. Positioned within the cylindricaltrough 18 is a screw conveyor 2O to the eX- tended shaft of which isattached a suitable pulley 21 adapted to be connected with anyconvenient source of power vto rotate the screw conveyor 20 and therebytransfer material from the feed hopper 19 to the interior of thebarrel1.

The lower end of the barrel 1 is closed by a transverse wall 22 havingspherical curva ture with its center of curvature located in the axis ofrotation of the barrel at the forward side of said wall. The wall 22 ispierced by a plurality of screening apertures 23 adapted to permit theescape of the fully pulverized material from the interior of the millwhile retaining the over size material for further grinding. The size,form and arrangement of the screening apertures 23 are subject to widevariation to suit the requirements of materials of dierent character andthe desired ineness of the product. These apertures 23 preferably expandoutwardly to prevent the lodgment therein of fragments of material andthe consequent choking of the screen.

As the fineness of grinding is directly related to the duration of timethe fragments of material are retained within the mill, the aXis of thebarrel l is inclined to such an angle with the horizontal that the rateof flow of the material longitudinally of the barrel will carry saidmaterial to the discharge end atthe precise moment it is pulverized tothe desired degree of iineness. Although I prefer to use a cylindricalbarrel with its axis suitably inclined to the horizontal, the form ofthe barrel may be subject to wide variation without departure from thespirit of my invention. Should the form of the barrel 1 be conicalinstead of cylindrical 'as shown, the inclination of the axis of`rotation must'be so adjusted as to produce the desired rate oflongitudinal flow of material within the barrel. Any increase ordecrease of the taper of the barrel would require an adjustment of theinclination of the axis of rotation moreor less closely approaching thehorizontal, and if the diameter of the discharge end of the barrel besutliciently increased it might be necessary to incline the axis ofrotation upwardly to prevent too rapid movement( of material through themill.

The friction of material against the sides of the barrel cause the lowerpart of the mass to'move upwardly with the ascending side of the barrelwhile the upper portion of the mass slides downward, maintaining acontinuous orbital movement of the fragments of'which the mass iscomposed, and the friction due to this movement is an important elementin producing the grinding action of the mill. The grinding balls, beingof greater specific gravity than the fragments of the material which isbeing pulvel-ized, gravitate toward the lower part of the mass andbecome buried beneath the lighter material. These balls are carriedupward with the side of the barrel to an elevation depending upon theangle of repose which is characteristic of the material under treatment,and to the centrifugal force due to the velocity of rotation. A t thepoint of maximum elevation the material falls away from the side of thebarrel and the grinding balls roll upon the surface of the mass.striking fragments of material lving upon the lower side of the barrelto break them by their percussive action, thereby materially assistingin pulverizing the material.

Vhen a mass composed of freely movable fragments of various size but ofthe same specific gravity is agitated. the finer particles tend to slipthrough the interstices between the larger fragments, and the largerfragments tend to tioat to the surface. resulting in a more or lesscomplete stratification of the mass relative to the size of itscomponent fragments. Due to this tendencv to stratification. andtheinclination of the lower side of the barrel. the finer particles ofmaterial sift to the bottom of the mass and travel longitndinalh7 of themill tending to accumulate against the surface of the screen. Owing tothe slippage of the material against the surfaces of the mill thisaccumulation of tine, material slides across the screening apertures asthe mass is carried upwardly and the smaller fragments are forcedthrough these apertures bv the weight of material ahove them. From thepoint of maximum elevation the material rolls downwardly. striking thesurface of the screen along lines approximately normal thereto, andsmall fragments are carried through the screening apertures withoutchange of direction. At the same time the larger and heavier fragments,together with the grindingballs, strike upon the surface of the lowerpart of the screen producing vibration therein which prevents thelodgment of material in the screening apertures.

As the larger fragments of material can only be broken by Contact withrelatively large and heavy grinding bodies, and the most efficientreduction of the liner particles is accomplished by a large number ofrelatively small grinding bodies, and as the size of the componentfragments of the material within the mill is progressively reduced as ittravels from the receiving towards the discharge end, it is apparentthat a corresponding classification of the grinding bodies is desirable.To accomplish such classification I have divided the barrel 1 into aseries of grinding compartments A, B, C and D by the transverse screens24, 25 and 26 which are similar to the screen 22 but are' respectivelyprovided with apertures of progressively decreasing dimensions, thescreens nearest the receiving end of the mill having the largestapertures. By this arrangement of screens the material in the successivecompartments is classified relative to the size of the componentfragment, and each grinding compartment may be provided with grindingbodies of a size appropriate to the most ethcient grinding of thematerial in said compartment.

I am aware that grinding mills have been proposed in which the interiorof the barrel is divided into a series of pulverizing chambers bytransverse lat screening partitions. Screens of this character haveproven to be extremely inefficient because the orbital path ofthefragments of materia-l is so nearly parallel .with the surface of thescreen that the line material on the forward side of the screen iscarried past the screening apertures and the pressure of materialagainst the rearward side of such a screen obstructs the passage ofmaterial therethrough. By the use of screening partitions of sphericalcurvature, such as are here illustrated, there is produced a moreetlicient screening action clue to the inclination of the active portionof the screeningsurface to the orbital path of the fragments of materialand to the peculiar action of the material at the back of such a screen.As the barrel revolves the material adiacentthe rearward side of thescreens 24, 25 and 26 is detiected rearwardly i tudinal iow of the finematerial, and by adding to the agitation of the material increasing theeffectiveness of the grindingtum bodies thereby still further improvingthe efficiency of the mill. Y

At the delivery end of the barrel 1 I have provided a receivingchamber27 having flanges 28 which form dust tight joints with the sides of thebarrel 1, and which is provided With a spout 29 through which thematerial vmay lescape from the receiving chamber to be disposed of inany preferred manner. Y

It will be understood that the broad features of this tube milland aspecies thereof different from the one hereinafter claimed, are coveredin the parent application above referred to. This application isdirected simply to one species of such av tube mill, which includes ascreen of the .character having a curvature, preferably spherical,transversely of the barrel.

1. In a pulverizing mill, the combination with an approximatelyhorizontal barrel adapted to revolve about its longitudinal axis, of atransverse Vscreen partition d ivid-' ing the interior of the barrelinto separate grindingv chambers said screen having a sphericadcurvature concentric with the axis of rotation'of the barrel.

- 2. A pulverizing mill comprising an approximately horizontal barrel, atransverse screen Vin said barrel having a- 4spherical curvature, saidscreenforming a inding, compartment within the "barrel anhaving lascreening surface s o inclined to the barrel wall that togethertherewith it supports the material within the com artment, andamultiplicity of'freely tumb ing crushing elements in said compartment.3. A pulverizing mill comprisin a barrel having its-wall inclined to thehorizontal so that material within the barrel will gravitate on the wallfrom one end of the barrel toward the other, said barrel being`revoluble about its longitudinal axis, a transverse screen forminglagrinding compartment curvature and serving together with a barrell wall:to support material 'in the grinding compartment, and a multiplicity offreely ling crushing elements in said compart ment. y v

.4.- A ulverizing mill comprising avbarrel having its wall inclinedtothe horizontal so that material within the barrel will gravitatefromone end toward the other on the barrel wall, said barrel being adaptedto rements.

volve about its longitudinal axis, a transverse screen forming a'grin'ding compartment in said barrel, said screen having a sphericalcurvature and serving together with a barrel wall to support material inthe grinding compartment, and a multiplicity' of reely tumbling crushingelements in said compartment, tlie interior of said .compartment beingfree from obstructions .to the assortment of'material.

5. A pulverizing mill comprising a barrel revoluble about itslongitudinal axis and having its wall inclined to the horizontal wherebymaterial will tend to gravitate thereon toward one end of the barrelasit revolves, a plurality of transverse screens in vsaid barrel forminggrinding compartments, said screens each having a spherical curvatureand serving together with the barrel wall to support material VAin agrinding compartment, and a multiplicity of freely tuinling crushingelementsv in said compartments.

6. A pulverizing mill comprising an approximately horizontal barrel, atransverse screen in said barrel curved transversely of the barrel, saidscreenl forming a grinding compartment within the barrel and havin vascreening surface so inclined to the barre Wall .that together therewithit supports .the material within the compartment, and amultiplicity. offreely tumbling crushing elements in said compartment. v 7. Apulverizing mill .comprising a barrel having its wall incline-d to thehorizontal so that material within the barrel will gravitate on the wallfrom one end of the barrel to ward the other, said barrel beingrevoluble about its longitudinal axis, a transverse screen forming agrinding compartment 1n vsaid barrel, said screen being curvedtransversely of the barrel and serving together with a barrel wall tosupport material inthe inding compartment, and a multiplicity of' lreely .tumbling crushing elements in said compartment. Y

8. A ulverizing mill comprising -a barrel revo uble about its`longitudinal axis and in\ivavingits wall inclined to the horizontal saidbarrel, said screen having a'spherical hereby material will vof thebarrel and serving together with the barrelwall to support material in agrinding com artment, and a multiplicity of freely tum ling crushingelements in said compartof the 'barrel as it In testimony whereof, Ialiix mysignature.

ALEXANDER n MAHAFFEY READ.

